1. Field of the Invention
The present invention relates to a deflection yoke for a Braun tube, and more particularly, to an improved deflection yoke for a Braun tube having a secondary 4-pole convergence yoke for correcting a misconvergence caused by the primary 4-pole convergence yoke, and to a fabrication method thereof.
2. Description of the Background Art
FIG. 1 shows a partial sectional view of a general color Braun tube, which includes an electron gun 4 emitting three electron beams from the rear side of a funnel 3, a screen 1 on which the electron beams collide to produce light, a shadow mask 2 discriminating the three electron beams and a deflection yoke 30 deflecting the electron beams to determined points of the screen 1.
The Braun tube serves to receive an electric signal from an external source for an image, changes it to a light signal and displays it as an image having a spatial position on the screen 1 and a functional content (color, luminosity).
Accordingly, in the Braun tube, the content signal having information of the color of an image to be displayed on the screen 1 is applied to the electron gun 4 so that a desired color is shown on the screen 1 through the appropriate color combination of R, G and B electron beams and R, G and B phosphors on the screen, and the position signal of the image is applied to the deflection yoke 30 so that the position points of the screen 1 that the R, G and B electron beams emitted from the electron gun 4 reach are controlled to display a desired image.
The deflection yoke 30 includes a horizontal deflection coil 31 deflecting the electron beams emitted from the electron gun of the Braun tube in the horizontal direction, a vertical deflection coil 33 deflecting the electron beams in the vertical direction, a conical ferrite core 34 for reducing loss of a magnetic force generated from the horizontal and the vertical deflection coils 31 and 33 to heighten the magnetic efficiency, and a holder 32 fixing the horizontal and the vertical deflection coils 31 and 33 and the ferrite core 34 at pre-set positions with respect to the Braun tube.
A primary 4-pole convergence yoke 35 and a ring-shaped permanent magnet 36 are installed at a neck portion 31 of the funnel 31 to correct a misconvergence caused due to a fabrication error of the deflection yoke 30 and the Braun tube.
As for the Braun tube, by varying the distance between the R beam and the B beam emitted from the electron gun 4, the curvature of the shadow mask 2 can be considerably reduced more than the inner curvature of a panel forming the screen 1, and thus, the hawling and doming characteristics of the Braun tube can be improved.
As shown in FIG. 2A, the primary 4-pole convergence yoke 35 is constructed such that coils are wound in the 2 o""clock, 5 o""clock, 7 o""clock and 10 o""clock positions to form magnetic fields as shown in FIG. 2B.
As shown in FIG. 3, in order to correct a misconvergence of a screen varied due to the primary 4-pole convergence yoke 35, a secondary 4-pole convergence yoke 40, on which auxiliary coils 41 are wound in the 12 o""clock, 6 o""clock, 3 o""clock and 9 o""clock positions, is provided at the ferrite core 34.
As shown in FIG. 4, in the deflection yoke, in order to apply a driving current to the primary and the secondary 4-pole convergence yokes 35 and 40, an amplifying circuit is connected in parallel with the vertical deflection coil 33 and an integrating circuit is connected in series with the vertical deflection coil 33. And in order to prevent an induced current from being generated in the secondary 4-pole convergence yoke 40, an induced current preventing circuit is provided to synchronize the parallelly connected horizontal deflection coil 31 and the serially connected horizontal compensation coil 51 to a vertical compensation coil 53.
The vertical compensation coil 53 is connected in series with the amplifying circuit and the integrating circuit and also connected in series with the secondary 4-pole convergence yoke 40.
The deflection yoke 30 constructed as described above supplies current generally having a frequency of 15.75 kHz or more to the horizontal deflection coil 31 which generates a deflecting magnetic field that deflects the electron beam in the Braun tube in the horizontal direction.
The deflection yoke 30 is formed to have a self-convergence form which is capable of converging the electron beams on a screen by applying a non-uniform magnetic field by the horizontal and vertical deflection coils 31 and 33 even when the three electron beam guns do not use any supplemental circuit or device.
In other words, in the deflection yoke, the winding distributions of the horizontal deflection coil 31 and the vertical deflection coil 33 are adjusted to form a barrel type or a pin-cushion type magnetic field by regions (an opening portion, a middle portion and a neck portion). Then, each of the three electron beams has a different deflection force according to its position, and thus, the electron beams are converged to the same point on the screen even from different distances of each beam from a starting point to an arrival point.
In addition, in the case where a magnetic field is formed by applying a current to the horizontal and the vertical deflection coils 31 and 33, it is difficult to deflect the electron beams over the entire screen only with the magnetic field applied by the horizontal and the vertical deflection coils 31 and 33. Thus, the ferrite core 34 is used to minimize the loss in the return path of the magnetic field, thereby heightening the magnetic field and increasing the magnetic force.
In the Braun tube, the howling and the doming characteristics of the shadow mask 2 may be degraded due to the planarization of the screen 1. Thus, after the primary 4-pole convergence yoke 35 is installed at the neck portion 3a of the funnel 3 to be symmetrical horizontally and vertically as shown in FIGS. 1 and 2, when the vertical deflection current (the current indicated by a dotted line in FIG. 5) supplied by the circuit illustrated in FIG. 4 is applied thereto, the magnetic fields B1 and B2 shown in FIG. 2B are formed at the primary 4-pole convergence yoke 35, so that the R beam receives a force in the 3 o""clock direction at the point xe2x80x98Axe2x80x99 and the B beam receives a force in the 9 o""clock direction.
At this time, on the screen 1xe2x80x3, the paths of the R beam and the B beam are not changed at the points xe2x80x98Bxe2x80x99 and Exe2x80x2, However, as shown in FIG. 5, at the points xe2x80x98Cxe2x80x99 and xe2x80x98Fxe2x80x99, the upper and lower end portions of the screen 1xe2x80x3, since the current flows in the opposite direction, a magnetic field is formed in the opposite direction to that of the magnetic field as shown in FIG. 2B. Accordingly, the R beam receives a force in the 9 o""clock direction and the xe2x80x98Bxe2x80x99 beam receives a force in the 3 o""clock direction, and thus, the positions of the R and the B beams are changed in the horizontal directions. As the beams trace other points of the screen 1xe2x80x3, the applied magnetic field is changed in proportion to the change in the beam position at the A-F points.
When the primary 4-pole convergence yoke 35 is operated, the distance between the R beam and the B beam at the center of the deflection yoke 30 is the longest at the point xe2x80x98Axe2x80x99 and the shortest at the points xe2x80x98Cxe2x80x99 and xe2x80x98Fxe2x80x99.
Meanwhile, the changes in the positions of the R beam and the B beam in the horizontal direction signify the change of the angle at which the R and the B beams are made incident on the shadow mask. In this respect, a small incident angle is called a grouping and a large incident angle is called a degrouping.
With reference to FIG. 7, the degree (G) of grouping is expressed by the following equation:
G=(3SQ/PhL)xe2x80x83xe2x80x83(1)
wherein xe2x80x98Sxe2x80x99 indicates a distance between the R and the B beams at the deflection center of the deflection yoke 30, xe2x80x98Qxe2x80x99 indicates a distance from the inner face of a panel 1xe2x80x2 to the shadow mask 2, xe2x80x98Ph, indicates a horizontal position on the shadow mask 2, and xe2x80x98Lxe2x80x99 indicates a distance from the deflection center of the deflection yoke 30 to the inner face of the panel 1xe2x80x99.
As noted in the above equation, as shown in FIG. 7, as the distance difference (S) between the R and the B beams becomes great at the point xe2x80x98Axe2x80x99 of the screen 1xe2x80x3 by operation of the primary 4-pole convergence yoke 35, the beam grouping degree is varied. A solution to this is to reduce the distance (Q) between the inner face of the panel 1xe2x80x2 to the shadow mask 2. Then, the beam grouping degree is not varied.
Thus, it can be noted that due to the variation of the distance difference (S) between the R and the B beam at the deflection yoke 30 produced by the primary convergence yoke 35, the distance (Q) from the inner face of the panel 1xe2x80x2 to the shadow mask 2 is shortest at the point xe2x80x98Axe2x80x99 of the screen 1xe2x80x3 and longest at the points xe2x80x98Cxe2x80x99 and xe2x80x98Fxe2x80x99.
That is, as the beam xe2x80x98Sxe2x80x99 value is varied by the magnetic field produced by the primary 4-pole convergence yoke 35, the distance (Q) from the inner face of the panel to the shadow mask 2 can be varied. Thus, the panel 10 and the shadow mask 2 may have the same curvature as shown in FIG. 8A, or the shadow mask 2 may have a smaller curvature than the inner curvature of the panel 10xe2x80x2 as shown in FIG. 8b, so that the hawling and doming phenomenon caused due to the planarized shadow mask 2 can be improved.
With reference to FIG. 7, xe2x80x98axe2x80x99 indicates a state that the xe2x80x98Sxe2x80x99 value is changed by the primary 4-pole convergence yoke 35, xe2x80x98bxe2x80x99 indicates a state that a convergence is compensated by the secondary 4-pole convergence yoke 40, and xe2x80x98cxe2x80x99 indicates a state that a static convergence is formed by the electron gun.
However, as for the Braun tube having the above-described deflection yoke, when the beam grouping degree is changed by the primary 4-pole convergence yoke 35, a misconvergence occurs on the screen.
In order to correct the misconvergence, the secondary 4-pole convergence yoke 40 having auxiliary coils 41 wound in the 12 o""clock, 6 o""clock, 3 o""clock and 9 o""clock directions of the ferrite core 34 is installed, to which a vertical deflection current indicated by the dotted line in FIG. 5 is applied. Then, as shown in FIG. 3B, magnetic fields (B3-B6) are formed in the opposite direction to the magnetic fields of the primary 4-pole convergence yoke 35 of FIG. 2B.
Accordingly, the R beam is deflected by the force (F4) of the magnetic field B5 at the point xe2x80x98Axe2x80x99 of the screen 1xe2x80x3 and is moved in the direction of 9 o""clock, and the B beam is deflected by the force (F3) of the magnetic field (B3) and is moved in the direction of 3 o""clock.
The R and the B beams are not moved at the points B and E of the screen. And as shown in FIG. 5, since the current direction at the points xe2x80x98Cxe2x80x99 and xe2x80x98Fxe2x80x99 of the screen are opposite to the current direction at the point xe2x80x98Axe2x80x99 of the screen, so that the magnetic fields are formed in the directions as shown in FIG. 3B and the R and the B beams are moved in the opposite direction to the point xe2x80x98Axe2x80x99 of the screen.
This is the opposite direction to the R and the B beams which are deflected by the magnetic fields B1 and B2 generated by the primary 4-pole convergence yoke 35, so that the secondary 4-pole convergence yoke 40 can correct the misconvergence of the beams on the screen generated by the primary 4-pole convergence yoke 35.
However, since the Braun tube of the conventional art mounts the secondary 4-pole convergence yoke 40 at the ferrite core 34, an induced electromotive force is generated at the auxiliary coil 41 of the ferrite core 34 by the magnetic field of the horizontal deflection coil 31 as shown in FIG. 9, and the magnetic field is generated to the auxiliary coil 41 in the direction of interfering with the horizontal deflection magnetic field by the induced electromotive force, generating a misconvergence on the screen.
In order to prevent occurrence of the misconvergence, as shown in FIG. 4, a circuit for preventing an induced current needs to be installed at the secondary 4-pole convergence yoke 40 by synchronizing the horizontal compensation coil 51 and the vertical compensation coil 53, which results in that the fabrication cost of products employing such a Braun tube is increased.
In addition, in the conventional Braun tube, the auxiliary coil 41 is wound on the ferrite core 34 by using an additional winding machine to construct the secondary 4-pole convergence yoke 40, which causes a problem that much time is taken for winding the auxiliary coil 41.
Moreover, when the secondary 4-pole convergence yoke 40 is combined with the ferrite core 34, the misconvergence on the screen is varied due to the combination dispersion, resulting in that its productivity is degraded and production cost is increased.
Therefore, an object of the present invention is to provide a deflection yoke for a Braun tube which is capable of preventing occurrence of an inverse-magnetic field due to an induced magnetic field and thus easily correcting a misconvergence of a screen by having a construction wherein a secondary 4-pole convergence yoke is mounted on a holder on which a deflection coil is wound, rather than at a ferrite core, or on a separate holder, and its fabrication method.
Another object of the present invention is to provide a deflection yoke for a Braun tube which is capable of improving assembly and productivity of a secondary 4-pole convergence yoke by winding or mounting the secondary 4-pole convergence yoke on a holder, and its fabrication method.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a deflection yoke for a Braun tube including a primary 4-pole convergence yoke adapted to be positioned at a neck portion of a funnel of a Braun tube and a secondary 4-pole convergence yoke adapted to be positioned in the vicinity of the funnel where horizontal and vertical deflection coils and a ferrite core are installed, for correcting a misconvergence generated due to the primary 4-pole convergence yoke, wherein at least one of the vertical and the horizontal deflection coils is wound on a first holder, and the secondary 4-pole convergence yoke is installed in such a manner that an auxiliary coil thereof is wound on at least one side of the inner side or the outer side of the first holder.
To achieve the above objects, there is also provided a deflection yoke for a Braun tube including a primary 4-pole convergence yoke adapted to be positioned at a neck portion of a funnel and a secondary 4-pole convergence yoke positioned in the vicinity of the funnel of a Braun tube where horizontal and vertical deflection coils and a ferrite core are installed, for correcting a misconvergence generated due to the primary 4-pole convergence yoke, wherein at least one of the vertical and the horizontal deflection coils is wound on a first holder, and a secondary 4-pole convergence yoke is installed having an auxiliary coil on a second holder which may be inserted into an inner side or on an outer side of the first holder.
To achieve the above objects, there is also provided a deflection yoke for a Braun tube including a primary 4-pole convergence yoke adapted to be positioned at a neck portion of a funnel of a Braun tube and a secondary 4-pole convergence yoke adapted to be positioned in the vicinity of the funnel where horizontal and vertical deflection coils and a ferrite core are installed, for correcting a misconvergence generated due to the primary 4-pole convergence yoke, wherein the secondary 4-pole convergence yoke is mounted on an outer side of the funnel.
To achieve the above objects, there is also provided a method for fabricating a deflection yoke for a Braun tube including a primary 4-pole convergence yoke adapted to be positioned at a neck portion of a funnel of a Braun tube and a secondary 4-pole convergence yoke adapted to be positioned in the vicinity of the funnel where horizontal and vertical deflection coils and a ferrite core are installed, for correcting a misconvergence generated due to the primary 4-pole convergence yoke, wherein the secondary 4-pole convergence yoke is fabricated in two steps by successively winding a coil in a flat form and bending both sides of the coil in the same direction to thereby form an auxiliary coil, and then insertedly mounting the auxiliary coil onto the inner side or the outer side of a holder where the secondary 4-pole convergence yoke is to be installed.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.